Field of the Invention
The invention relates to a method for the manufacture of highly integrated circuits on a semiconductor substrate in which a wafer of semiconductor material is coated on both sides with at least one deposition process and in which the coating on the back of the wafer is subsequently removed again by etching being carried out with the front of the wafer being free of lacquer.
During the manufacturing process of the semiconductor components, the wafers, which are normally formed of silicon, are subjected again and again to deposition processes during which the wafers are coated on both sides depending on the method and/or on the system. They are essentially oxidations (thermal oxide), as well as CVD (chemical vapor deposition) processes (polysilicon doped and undoped, silicon dioxide, silicon nitride). Since the build up of several different layers on the back of the wafer is not desired and can lead to adverse effects on other processes, etching steps are carried out on the back during the course of the entire production process. The way that usually occurs is that the front is lacquered over its entire surface and afterward the current layer on the back of the wafer is removed again by means of a wet or dry etching procedure. The Tokuda CDE 7, CDE 8 or Gasonics IPC are used, for example, as the plasma etching equipment. Thereafter, the lacquer on the front of the wafer has to be removed again. The additional step of coating and removing the coating from the front of the wafer that occurs in that back etching known in the art requires processing time, system capacity (lacquering line, lacquer removal basins or O.sub.2 -plasma stripper, and cleaning), as well as use of a considerable amount of chemicals.
In the meantime, however, another etching method on a wet chemical basis which has become known in the art is carried out without front lacquering. The manufacturer of that equipment (RST-100) is the firm SEZ in Villach, Austria. In that method, the silicon wafers, which are already provided with structures for the most part, are turned quickly with their surfaces, in other words the fronts of the wafers, facing downward on a rotating air cushion, while the wet-chemical etching solution flows down on the back of the wafer. The quick rotation of the wafer causes the chemicals to be spun out over the edge of the back of the wafer and they therefore cannot come in contact with the front side.
However, that known method is connected with considerable problems since, on one hand, the requirement of rotating a semi-processed silicon wafer with its surface downward on an air cushion safe from contact and the damage associated with it requires a complicated and therefore vulnerable mechanical system. On the other hand, blowing on the open front side of the wafer in semiconductor production is normally to be avoided as far as possible to prevent particulate pollution resulting from the turbulence processes. Moreover, the amount of chemicals consumed in that known method is naturally very high, since due to the spinning process on the back of the wafer, a continuous flow is necessary. However, high chemical consumption should be avoided due to environmental reasons.